Magnetic sheet composition, magnetic sheet, and method for producing magnetic sheet

ABSTRACT

To provide a magnetic sheet composition, which contains: a binder; magnetic powder; and a curing agent, wherein the binder contains a thermosetting organic resin, and the curing agent contains a sulfonium borate complex expressed by General Formula 1: 
     
       
         
         
             
             
         
       
     
     where R 1  is an aralkyl group, R 2  is a lower alkyl group, X is a halogen atom, and n is an integer of 0 to 3.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional of application Ser. No. 12/854,472, filed Aug. 11,2010, which is a Continuation of International Application No.PCT/JP2009/052720, filed on Feb. 17, 2009, which claims priority fromJapanese Patent Application No. 2008-036349, filed Feb. 18, 2008, theentire content of each of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic sheet, which is capable ofsuppressing undesirable electromagnetic waves emitted from an electronicequipment, and inhibiting electromagnetic disorders caused due to theinterference of the undesirable electromagnetic waves, and also relatesto a production method thereof which is efficient and low cost.

2. Description of the Related Art

The magnetic sheets are used for depression of noise, or for RFID. Forthe purpose of depression of noise, along with rapid developments ofelectronic equipments, e.g. personal computers and mobile phones, suchas down sizing and higher frequency, these electronic equipments sufferfrom a noise interference due to outer electromagnetic waves andinterference of noises occurred within the electronic equipment. Inorder to suppress such interferences, various countermeasures have beentaken for the noises. For example, a magnetic sheet (noise depressingsheet) is disposed adjacent to a noise emitting source or a noisereceiving source.

The magnetic sheet is formed by adding alloy (magnetic powder) such asFe—Si—Al to an epoxy resin, acrylic resin, or the like, and then beingcured to form into a sheet by hot pressing. The magnetic powder inhibitsnoise, and functions as a so-called noise depressor. The better theeffect of inhibiting the noise of the magnetic sheet is, the larger animaginary part μ″ of the magnetic permeability of the magnetic sheet is.

On the other hand, in the case where the magnetic sheets are used forRFID, as a recent trend in the art, radio communication using a coilantenna in an electromagnetic induction method, which is represented asmobile information terminals having IC tags referred as Radio FrequencyIdentification (RFID), has been widely used. For example, in the mobileinformation terminal, various conductors (metals) such as a metal casingor metal parts are disposed adjacent to an antenna element fortransmitting and receiving due to downsizing of the mobile informationterminal. In this case, a magnetic field usable for the transmission islargely attenuated because of the metal present adjacent to the antennaelement, and as a result, a communication distance for RFID transmissionin an electromagnetic induction system may be shortened, or transmissionor receiving of a radio frequency may become difficult because aresonance frequency is shifted. To prevent these electromagneticdisorders, a magnetic sheet is placed between the antenna element andthe conductor. As for a function of RFID, it is preferred that themagnetic sheet has a large real part μ′ of the magnetic permeability,and a small imaginary part μ″ of the magnetic permeability.

A curing agent (i.e. a crosslinking agent) for curing a thermosettingorganic resin is generally added to a magnetic sheet composition that isa material of the magnetic sheet. The magnetic sheet is hardened byadding the curing agent to the magnetic sheet composition. Especially inthe case where a polymer material for use in the magnetic sheet easilyabsorbs moisture, however, the thickness of the magnetic sheetundesirably changes depending on the fluctuations in the environmentsuch as temperature and humidity. In order to sufficiently cure themagnetic sheet in such environment, the curing temperature is set highand the curing duration is set long. In this case, a large volume ofwater is consumed as the cooling duration becomes long according to thelong and high temperature curing, and moreover the production efficiencydecreases. If the curing temperature is set high and the curing durationis set short to solve the aforementioned problem, a problem occurs inthe heat resistance of an insulating support.

Moreover, a sulfonium-based cationic curing agent has been commonly usedas the conventional curing agent, but the sulfonium-based cationiccuring agent contains antimony that is toxic. Therefore, use of suchcuring agent gives an adverse influence to the environment. Furthermore,as in this antimony-containing sulfonium-based cationic curing agent, acounter ion has a Sb—F bond, which has weak bonding force, a F⁻¹ iontends to be free. For this reason, in the case where the magnetic sheetcontaining the antimony-containing cationic curing agent is used arounda wiring, the free F⁻¹ ion reacts with water to form hydrofluoric acid,which causes corrosion of the wiring.

For example, Japanese Patent Application Laid-Open (JP-A) No. 2007-95829describes photocuring of a magnetic binder containing a photocuringcationic curing agent, and discloses an electromagnetic-wave-absorbingsheet having a concentration distribution of magnetic filler from thesurface of the sheet towards the depth direction thereof. The curing ofthis electromagnetic-wave-absorbing sheet is performed by a drum device.

BRIEF SUMMARY OF THE INVENTION

The present invention aims at solving the problems in the art, andachieving the following objects. Namely, an object of the presentinvention is to provide a magnetic sheet composition, which is amaterial of a magnetic sheet, capable of reducing unnecessaryelectromagnetic waves released from an electronic equipment, is capableof inhibiting electromagnetic disorders caused by an interference ofunnecessary electromagnetic waves within an electronic equipment,prevents liberation of halogen ions to thereby prevent corrosion ofwirings when it is used around the wirings, and does not give anyadverse influence to the environment. Another object of the presentinvention is to provide a method for producing a magnetic sheet usingsuch magnetic sheet composition, and a magnetic sheet produced by suchmethod for producing a magnetic sheet.

The inventors of the present invention have intensively studied to solvethe problems, and come to the following insights. Namely, the inventorshave found a magnetic sheet composition containing at least a binderwhich contains a thermosetting organic resin, a magnetic powder, and acuring agent which contains a sulfonium borate complex expressed byGeneral Formula 1 can produce a magnetic sheet which realizeslow-temperature-high-speed curing, prevents libration of halogen ions soas to prevent corrosion of wirings when it is used around the wirings,gives less environmental load.

In General Formula 1, R₁ is an aralkyl group, R₂ is a lower alkyl group,X is a halogen atom, and n is an integer of 0 to 3.

The present invention has been made based upon the insight of thepresent inventors, and means for solving the aforementioned problems areas follows.

<1> A magnetic sheet composition, containing:

a binder;

magnetic powder; and

a curing agent,

wherein the binder contains a thermosetting organic resin, and thecuring agent contains a sulfonium borate complex expressed by GeneralFormula 1;

where R₁ is an aralkyl group, R₂ is a lower alkyl group, X is a halogenatom, and n is an integer of 0 to 3.

Since the magnetic sheet composition according to <1> contains thecuring agent, which does not contain antimony, it will provide a lessload to the environment. Moreover, as the bonding energy of X (halogenatom) and a phenyl group in the sulfonium borate complex expressed byGeneral Formula 1, the bond between X (halogen atom) and the phenylgroup is unlikely broken, and thus the isolation of X (halogen atom)ions is prevented. Therefore, the generation of acid such ashydrofluoric acid as a result of the reaction between free X (halogenatom) ions and water or the like is prevented. For this reason,corrosion of wirings can be prevented even when a magnetic sheet formedusing the magnetic sheet composition is used around the wirings.Furthermore, a cationic curing magnetic sheet curable at low temperatureand at high speed can be provided.

<2> The magnetic sheet composition according to <1>, wherein R₁ is abenzyl group, an o-methyl benzyl group, or a (1-naphthyl)methyl group.<3> The magnetic sheet composition according to any of <1> or <2>,wherein R₂ is a methyl group.<4> The magnetic sheet composition according to any one of <1> to <3>,wherein the sulfonium borate complex is contained in an amount of 2parts by mass to 15 parts by mass relative to 106.1 parts by mass of thebinder.<5> The magnetic sheet composition according to any one of <1> to <4>,further containing a flame retardant, wherein the flame retardantcontains carboxylic acid amide-containing melamine cyanurate.<6> A method for producing a magnetic sheet, containing:

applying the magnetic sheet composition as defined in any one of <1> to<5> onto a substrate;

drying the magnetic sheet composition applied onto the substrate; and

thermosetting the dried magnetic sheet composition.

<7> The method for producing a magnetic sheet according to <6>, furthercontaining:

stacking a convex-concave forming layer and a pattern transferring layeron a surface of a magnetic layer, which is formed by thermosetting themagnetic sheet composition, in this order from the side of the magneticlayer so as to form a stacked body; and

hot-pressing the stacked body so as to transfer a surface configurationof the pattern transferring layer to surfaces of the convex-concaveforming layer and the magnetic layer, as well as bonding theconvex-concave forming layer and the magnetic layer together.

<8> A magnetic sheet, obtained by the method as defined in any of <6> or<7>.

In accordance with the present invention, the various problems in theart can be solved, and there can be provided a magnetic sheetcomposition, which is a material of a magnetic sheet, capable ofreducing unnecessary electromagnetic waves released from an electronicequipment, is capable of inhibiting electromagnetic disorders caused byan interference of unnecessary electromagnetic waves within anelectronic equipment, prevents libration of halogen ions to therebyprevent corrosion of wirings when it is used around the wirings, anddoes not give any adverse influence to the environment, as well asproviding a method for producing a magnetic sheet using such magneticsheet composition, and a magnetic sheet produced by such method forproducing a magnetic sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a ¹H-NMR chart of the sulfonium borate complex expressed bythe formula 1a.

FIG. 2 is a ¹H-NMR chart of the sulfonium borate complex expressed bythe formula 1b.

FIG. 3A is a photograph showing a cross-section of the magnetic sheetsample (Example 1) after the corrosion test.

FIG. 3B is a photograph showing a cross-section of the magnetic sheetsample (Comparative Example 8) after the corrosion test.

FIG. 4 is a diagram for explaining the method for measuring thetransmission loss.

DETAILED DESCRIPTION OF THE INVENTION (Magnetic Sheet Composition)

The magnetic sheet composition of the present invention contains atleast a binder, a magnetic powder, and a curing agent, and may furthercontain other components, if necessary.

—Curing Agent—

The curing agent is suitably selected depending on the intended purposewithout any restriction, provided that it contains the sulfonium boratecomplex expressed by General Formula 1:

In General Formula 1, R₁ is an aralkyl group, R₂ is a lower alkyl group,X is a halogen atom, and n is an integer of 0 to 3.

Examples of the aralkyl group expressed as R₁ include a benzyl group, ano-methyl benzyl group, a (1-naphthyl)methyl group, a pyridyl methylgroup, and an anthracenyl methyl group. Among them, the(1-naphthyl)methyl group is preferable as it provides the curing agentwith excellent and fast curing ability, and it is readily available.

Examples of the lower alkyl group expressed as R₂ include a methylgroup, an ethyl group, a propyl group, and a butyl group. Among them,the methyl group is preferable as it provides the curing agent withexcellent and fast curing ability, and it is readily available.

“n” is an integer of 0 to 3, where n denotes a number of hydroxylgroup(s) contained in phenyl group(s) bonded to the sulfonium residue.In the case where n is 1, examples of such phenyl group include a4-hydroxyl phenyl group, a 2-hydroxyl phenyl group, and a 3-hydroxylphenyl group. In the case where n is 2, examples of such phenyl groupinclude a 2,4-dihydroxyl phenyl group, a 2,6-dihydroxyl phenyl group, a3,5-dihydroxyl phenyl group, and a 2,3-dihydroxyl phenyl group. In thecase where n is 3, examples of such phenyl group include a2,4,6-trihydroxy phenyl group, a 2,4,5-trihydroxy phenyl group, and a2,3,4-trihydroxy phenyl group. Among them, the 4-hydroxy phenyl group ispreferable, as it provides the curing agent with excellent and fastcuring ability, and it is readily available.

Examples of the halogen atom expressed as X include a fluorine atom,chlorine atom, bromine atom, and iodine atom. Among them, the fluorineatom having high electron-withdrawing properties is preferable forimproving the reactivity.

The sulfonium borate complex expressed by General Formula 1 can beproduced in accordance with the following reaction formula. In GeneralFormulae 1 to 3, R₁ is an aralkyl group, R₂ is a lower alkyl group, X isa halogen atom, and n is an integer of 0 to 3.

Namely, the sulfonium antimonate complex (see JP-A No. 10-245378 for asynthesis method thereof) expressed by General Formula 2 is madedissolved in an organic solvent such as ethyl acetate, and a solution ofsodium borate (see JP-A No. 10-310587 for a synthesis method thereof)expressed by General Formula 3 is mixed to the aforementioned solutionin the equimolecular amount. The obtained two-layered mixture is stirredat the temperature of 20° C. to 80° C. for 1 hour to 3 hours so as toallow the sulfonium antimonate complex expressed by General Formula 2 toreact with the sodium borate expressed by General Formula 3 to therebyobtain a sulfonium borate complex expressed by General Formula 1. Theisolation of the sulfonium borate complex expressed by General Formula 1can be performed in the following manner. Specifically, the organicsolvent layer is separated and dried, and the organic solvent isevaporated to remove under the reduced pressure so that the specifiedsubstance can be obtained as the evaporated residue.

The sulfonium borate complex expressed by General Formula 1 can be usedas a thermal cationic polymerization initiator for a common epoxy resin.In this case, an epoxy resin composition (in the form of a paste orfilm) containing 100 parts by mass of an epoxy resin and 0.1 parts bymass to 10 parts by mass of the sulfonium borate complex expressed byGeneral Formula 1 as the thermal cationic polymerization initiator isheated at 50° C. to 150° C. so as to provide a cured product which isexcellent in electrolytic corrosion resistance, and is cured at highspeed and low temperature.

—Binder—

The binder is suitably selected depending on the intended purposewithout any restriction. Examples thereof include acrylic rubbercontaining a thermosetting organic resin, which will be mentioned later.

The acrylic rubber preferably contains epoxy groups. In this case, theepoxy groups are reacted with a curing agent, so as to improvereliability. Moreover, the acrylic rubber preferably further containshydroxyl groups. The hydroxyl groups are contained in the acrylicrubber, so as to improve adhesion.

The mass average molecular mass of the acrylic rubber is 10,000 to450,000 in terms of excellent coating ability.

When the mass average molecular mass is less than 10,000, the viscosityof the magnetic sheet composition decreases, and it becomes hard toapply the magnetic sheet composition containing the magnetic powderhaving a large mass. When the mass average molecular mass is more than450,000, the viscosity of the magnetic sheet composition becomes large,and it becomes hard to apply the magnetic sheet composition having alarge viscosity.

The glass transition temperature of the acrylic rubber is preferably−50° C. to +15° C.

When the glass transition temperature is lower than −50° C., thereliability at a high temperature or in a high temperature and highhumidity environment may become poor. When the glass transitiontemperature is higher than +15° C., the magnetic sheet tends to be hard.

Moreover, one or more acrylic rubbers may be used in combination.

——Thermosetting Organic Resin——

Examples of the thermosetting organic resin include an epoxy resin. Whenan epoxy resin having a small molecular mass is added, the meltviscosity of the binder is further decreased upon compressing (forming)the magnetic sheet. Thus, the magnetic properties can be increased.Moreover, for example, by using a polyfunctional epoxy resin, thereliability of the magnetic sheet after curing can be further improved.

Examples of the epoxy resin include a cation-curing epoxy resin. Theepoxy resin may be used independently, or in combination.

—Magnetic Powder—

The magnetic powder is suitably selected depending on the intendedpurpose without any restriction. Examples of the shape of the magneticpowder include a flat, lump, fiber, sphere, and irregular shape. Ofthese, the flat shape is preferable as the magnetic powder of such shapecan be easily orientated in a predetermined direction and high magneticpermeability can be attained.

Examples of the magnetic powder include soft magnetic metal, ferrite,and pure iron particles.

Examples of the soft magnetic metal include magnetic stainless steel(i.e., Fe—Cr—Al—Si Sendust (i.e., Fe—Si—Al alloy), permalloy (i.e.,Fe—Ni alloy), silicon copper (i.e., Fe—Cu—Si alloy), Fe—Si alloy,Fe—Si—B(—Cu—Nb) alloy, Fe—Ni—Cr—Si alloy, Fe—Si—Cr alloy, Fe—Si—Al—Ni—Cralloy, and amorphous metal.

The magnetic powder may be used independently, or in combination.

The amounts of the binder, magnetic powder, and curing agent are eachsuitably selected depending on the intended purpose without anyrestriction. It is preferred that the amount of the magnetic powder be400 parts by mass to 1,400 parts by mass and the amount of the sulfoniumborate complex as the curing agent be 2 parts by mass to 15 parts bymass, both relative to 106.1 parts by mass of the binder. Note that, theproportion of the magnetic powder in the magnetic sheet is preferably60% by weight to 95% by weight.

When the amount of the magnetic powder is less than 400 parts by massrelative to 106.1 parts by mass of the binder, excellent magneticproperties may not be obtained. When the amount thereof is more than1,400 parts by mass relative to 106.1 parts by mass of the binder, itbecomes hard to bind the magnetic powder with the binder. Consequently,the thickness variation of the magnetic sheet becomes large in a hightemperature and high humidity environment, and the flame retardant maybleed out on the surface of the magnetic sheet. Moreover, the magneticsheet becomes brittle, and the magnetic powder falls off (powderfalling) not only from an edge face of the magnetic sheet but also froma surface of the magnetic sheet.

—Other Components—

The other components are suitably selected from various known additivesdepending on the intended purpose without any restriction, as long asthe effect of the present invention is not impaired. For the purpose ofimproving the coating ability (i.e. adjusting the viscosity) of amagnetic composition, which is prepared by adding the magnetic powderand the flame retardant to the binder, a solvent may be added. Examplesof the solvent include: ketenes such as acetone, methylethyl ketone,methylisobutyl ketone, and cyclohexanone; alcohols such as methanol,ethanol, propanol, butanol, isopropyl alcohol; esters such as methylacetate, ethyl acetate, propyl acetate, butyl acetate, ethyl lactate,and ethyl glycol acetate; ethers such as diethylene glycol dimethylether, 2-ethoxy ethanol, tetrahydrofurane, and dioxane; aromatichydrocarbon compounds such as benzene, toluene, and xylene; andhalogenated hydrocarbon compounds such as methylene chloride, ethylenechloride, carbon tetrachloride, chloroform, chlorobenzene. These may beused independently or in combination.

If necessary, various additives, such as a flame retardant (e.g.melamine cyanurate, and red phosphorous), a dispersant, stabilizer,lubricant, silane or titanate coupling agent, filler, plasticizer, andantioxidant may be added.

The amounts of the other components are suitably selected depending onthe amounts of the binder, the magnetic powder and the curing agent,without any restriction.

——Carboxylic Acid Amide-Containing Melamine Cyanurate——

The presence of the carboxylic acid amide in the carboxylic acidamide-containing melamine cyanurate can be confirmed, for example, bypyrolysis gas chromatography analysis (Py-GC-MS).

The number average particle size of the carboxylic acid amide-containingmelamine cyanurate is suitably selected depending on the intendedpurpose without any restriction. It is preferably 1 μm or less.

When the number average particle size is more than 1 the close alignmentof the magnetic powder is blocked, and the magnetic properties of themagnetic sheet may be degraded, and the thickness variation of themagnetic sheet may become large at high temperature or in a hightemperature and high humidity environment.

The number average particle size of the carboxylic acid amide-containingmelamine cyanurate can be obtained, for example, from a particle sizedistribution thereof measured by laser diffraction.

The carboxylic acid amide-containing melamine cyanurate may be acommercially available product or arbitrarily prepared product.

Examples of the commercially available product include MC-5F(manufactured by SAKAI CHEMICAL INDUSTRY, CO., LTD.).

A method for producing the carboxylic acid amide-containing melaminecyanurate is suitably selected depending on the intended purpose withoutany restriction. For example, a method for treating a surface of themelamine cyanurate using fatty acid is preferably used.

A surface treatment method is suitably selected from known methodsdepending on the intended purpose without any restriction. For example,a method of mixing and stirring the melamine cyanurate and the fattyacid is used.

When the surface of the melamine cyanurate is treated with the fattyacid, it is considered that an amino group in the melamine cyanurate isreacted with the fatty acid, and as a result, an amide compound isformed, as represented by the following reaction formula 1. Thus, ananalysis is performed by pyrolysis gas chromatography (Py-GC-MS), so asto confirm the presence of the carboxylic acid amide.

—NH₂+R—COOH→R—CONH—  Reaction Formula 1

The fatty acid is suitably selected depending on the intended purposewithout any restriction. Examples thereof include lauric acid,isostearic acid, stearic acid, palmitic acid, oleic acid, and linolenicacid. These may be used independently, or in combination. Among these,lauric acid is preferred, in terms of high hydrophobicity and favorabledispersibility.

——Red Phosphorus——

The flame retardant preferably contains red phosphorus, in addition tothe silicon atom-containing melamine cyanurate and the carboxylic acidamide-containing melamine cyanurate. This is advantageous in terms offurther improving the flame retardant of the magnetic sheet.

The red phosphorus is suitably selected depending on the intendedpurpose without any restriction, and may be a commercially availableproduct or arbitrarily prepared product. It is preferred that thesurface of the red phosphorus be coated for providing excellent humidityresistance, and favorable stability owing to no spontaneous combustionupon mixing.

As the red phosphorus whose surface is coated, red phosphorus whosesurface is treated with aluminum hydroxide is exemplified.

The amount of the red phosphorus is suitably selected depending on theintended purpose without any restriction. It is preferably 6 parts bymass to 19 parts by mass, relative to the 100 parts by mass of thebinder.

When the amount is less than 6 parts by mass, the obtainable effect ofimproving the flame resistance cannot be obtained. When the amount ismore than 19 parts by mass, the total amount of the magnetic powder andthe flame retardant increases relative to the binder. This makesdifficult to keep binding the magnetic powder and the flame retardanttogether with the binder, the proportion of the magnetic powder in themagnetic sheet is decreased, causing decrease in the magneticpermeability.

The method for producing a magnetic sheet of the present invention issuitably selected from those known in the art depending on the intendedpurpose without any restriction, but the magnetic sheet is suitablyproduced by the following method.

<Production Method>

The method for producing a magnetic sheet contains at least applying themagnetic sheet composition on a substrate, drying the magnetic sheetcomposition applied on the substrate, and thermosetting the driedmagnetic sheet composition, and may further contain other steps, ifnecessary.

—Magnetic Sheet Composition—

The magnetic sheet composition contains at least a binder, a magneticpowder, and a curing agent, and may further contain other components. Inthe magnetic sheet composition, the binder contains a thermosettingorganic resin, and the curing agent contains a sulfonium borate complexexpressed by General Formula 1.

Note that, the details of the binder, magnetic powder, curing agent, andother components are as mentioned above.

—Substrate—

The substrate is suitably selected depending on the intended purposewithout any restriction, but it is preferably a polyester film a surfaceof which is lubrication processed (a release PET) as the formed magneticlayer can be easily peeled from the substrate.

—Coating—

A method for coating is suitably selected depending on the intendedpurpose without any restriction. Examples thereof include spin coating,dip coating, kneader coating, curtain coating, blade coating, and doctorblade coating. Of these, the blade coating, and the doctor blade coatingare preferable, in terms of excellent coating efficiency.

—Drying—

A method for drying is suitably selected depending on the intendedpurpose without any restriction. Examples thereof include methods usinga dry oven, a drier, a hot press, and a heating automation. Among them,the method using the dry oven is particularly preferable as the processthereof is easy, and it is advantageous in terms of the cost for thefacilities.

—Thermosetting (Formation)—

A method of thermosetting (forming) the magnetic sheet is suitablyselected depending on the intended purpose without any restriction. Forexample, the magnetic sheet can be formed by hot pressing.

A method of hot pressing is suitably selected depending on the intendedpurpose without any restriction. For example, both sides of a layer,which is formed by applying the magnetic composition onto the substrate,are sandwiched with press plates respectively via buffer materials, andheated and pressed.

The conditions for the hot pressing are suitably adjusted depending onthe intended purpose without any restriction. For example, thetemperature is preferably 80° C. to 190° C., the pressure is preferably5 MPa to 20 MPa, and the duration is preferably 1 minute to 20 minutes.

The structure, thickness, and material of the buffer material aresuitably selected depending on the indented purpose without anyrestriction.

The buffer material may be a commercially available product orarbitrarily prepared product. Examples of the commercially availableproduct include a high quality paper (product name: OK Prince HighQuality 70, manufacturer: Oji Paper Co., Ltd., Bekk smoothness: 6.2sec/mL), a cushioned paper (product name: TF190, manufacturer: THE TOYOFIBRE CO., LTD., Bekk smoothness: 1.7 sec/mL), nylon mesh (product name:N-NO. 1105, manufacturer: TOKYO SCREEN CO., LTD., Bekk smoothness: lessthan 0.1 sec/mL), cotton cloth (product name: Kanakin No. 3,manufacturer: Japanese Standards Association, Bekk smoothness: less than0.1 sec/mL), a base paper for an adhesive (product name: SO base paper18G, manufacturer: DAIFUKU PAPER MFG CO., LTD., Bekk smoothness: lessthan 0.1 sec/mL), a double sided release paper (product name: 100GVW(High lubricity surfaces), manufacturer: Oji Paper Co., Ltd., Bekksmoothness: 146 sec/mL), and a double sided release paper (product name:100GVW (Low lubricity surfaces), manufacturer: Oji Paper Co., Ltd., Bekksmoothness: 66 sec/mL).

Bekk smoothness expresses the time required for a certain amount of airto pass through the surface having some irregularities of a sheet membersuch as paper and a cloth. The larger the degree of the irregularitieson the surface of the sheet member, the smaller the value of Bekksmoothness is, namely meaning excellent “lubricity”.

Bekk smoothness is measured, for example, by Bekk Smoothness Tester(manufactured by TESTER SANGYO CO., LTD.).

As mentioned above, the magnetic sheet composition is applied onto thesubstrate, the applied magnetic sheet composition on the substrate isdried, and the dried magnetic sheet composition is thermoset, to therebyproduce a magnetic sheet. Here, the magnetic sheet is obtained in such astate that the magnetic sheet is laminated on the substrate (releasePET), but the magnetic sheet can be peeled from the substrate and used.

—Other Steps—

Other steps are suitably selected depending on the intended purposewithout any restriction. Examples thereof include a pattern-transferringstep.

——Pattern-Transferring Step——

The pattern transferring step is stacking a convex-concave forming layerand a pattern transferring material on a surface of the magnetic layer,which has been formed by thermosetting the magnetic sheet composition,in this order, and hot pressing the stacked layers so as to bond theconvex-concave forming layer with the magnetic layer to form a stackedbody, as well as to transfer a surface configuration of the patterntransferring material to a surface of the laminate of the convex-concaveforming layer and the magnetic layer.

———Convex-Concave Forming Layer———

The structure, thickness, and material of the convex-concave forminglayer are suitably selected depending on the intended purpose withoutany restriction. The details thereof are as mentioned earlier.

The surface configuration of the convex-concave forming layer is notparticularly limited, and one surface thereof may be surface-treated, orno surface treatment may be performed. As a surface treatment, a matteprocessing, lubrication processing without using a silicone resin andthe like are preferable. In the case a surface thereof is treated withany of the aforementioned processes, a lubricity of the surface isimproved compared to the surface without any surface treatment.Moreover, in these processes of the surface treatment, as the siliconeresin is not used, silicone oligomers do not bleed out under thecondition of high temperature and/or high humidity, and thus it issuitably used inside of an electronic equipment.

The matte processing is suitably selected depending on the intendedpurpose without any restriction. Examples thereof include a sand matteprocessing, chemical matte processing, surface emboss processing and thelike. By these processing, the convex-concave pattern is formed on theconvex-concave forming layer and as a result, a lubricity thereof isimproved.

The convex-concave forming layer preferably has Bekk smoothness of 200sec/mL or less before hot pressing.

When Bekk smoothness thereof is more than 200 sec/mL before hotpressing, it adversely affects Bekk smoothness after hot pressing.

—Pattern-Transferring Material—

The structure, thickness and material of the pattern-transferringmaterial are suitably selected depending on the intended purpose withoutany restriction. For example, those having a convex-concave pattern onthe surface thereof and excellent air permeability are preferable. Inthis case, once the convex-concave pattern convex-concave forming layeron the surface of the pattern transferring material is transferred tothe convex-concave forming layer, the convex-concave pattern is formedon the surface of the convex-concave forming layer, and as a result,Bekk smoothness of the convex-concave forming layer is lowered andlubricity of the convex-concave forming layer is improved.

The surface irregularities of the pattern transferring material can beevaluated by the value of Bekk smoothness. The smaller the value of Bekksmoothness is the larger the irregularities are.

The structure of the pattern transferring material may be a monolayeredstructure or laminate structure.

The thickness of the pattern transferring material is preferably 25 μmto 200 μm.

When the thickness thereof is less than 25 μm, it may not be able toattain a magnetic sheet of low Bekk smoothness. When the thicknessthereof is more than 200 μm, heat does not easily transfer to themagnetic layer at the time of hot pressing, and thus the reliability maybe lowered.

The material of the pattern transferring material is, for example,paper, synthetic fibers, or natural fibers.

The pattern-transferring material may be a commercially availableproduct or arbitrarily prepared product. Examples of the commerciallyavailable product include a high quality paper (product name: OK PrinceHigh Quality 70, manufacturer: Oji Paper Co., Ltd., Bekk smoothness: 6.2sec/mL), a cushioned paper (product name: TF190, manufacturer: THE TOYOFIBER CO., LTD., Bekk smoothness: 1.7 sec/mL), nylon mesh (product name:N-NO. 110S, manufacturer: TOKYO SCREEN CO., LTD., Bekk smoothness: lessthan 0:1 sec/mL), cotton cloth (product name: Kanakin No. 3,manufacturer: Japanese Standards Association, Bekk smoothness: less than0.1 sec/mL), a base paper for an adhesive (product name: SO base paper18G, manufacturer: DAIFUKU PAPER MFG CO., LTD., Bekk smoothness: lessthan 0.1 sec/mL), a double sided release paper (product name: 100GVW(High lubricity surfaces), manufacturer: Oji Paper Co., Ltd., Bekksmoothness: 146 sec/mL), and a double sided release paper (product name:100GVW (Low lubricity surfaces), manufacturer: Oji Paper Co., Ltd., Bekksmoothness: 66 sec/mL).

———Arrangement of Stacked Layers———

The method for an arrangement of stacked layers is suitably selecteddepending on the purpose without any restriction, provided that theconvex-concave forming layer and the pattern transferring material arestacked on at least one surface of the magnetic layer in this order. Itis preferred that a release layer and the pattern transferring materialare further stacked on the other surface of the magnetic layer in thisorder. As the pattern transferring material are stacked on the othersurface of the magnetic layer with the release layer being placed inbetween, the other surface of the magnetic layer is protected andprevented from closely attaching to the pattern transferring material atthe time of hot pressing mentioned later, and the pattern transferringlayer is easily peeled from the magnetic layer along with the releaselayer after hot pressing. Moreover, the surface configuration of thepattern transferring material is transfer to the surface of the magneticlayer which is present at the side of the releasing layer, and at thistime, air bubbles present in the resin composition of the magnetic layerare easily released, and thus the reliability of the obtained magneticsheet is improved. In the case where the pattern transferring materialis not used at the side of the release layer, magnetic permeability ofthe magnetic sheet is improved.

The release layer is suitably selected, depending on the intendedpurpose without any restriction, provided that it functions to preventthe close attachment between the other surface of the magnetic layer andthe pattern transferring material at the time of hot pressing. Therelease layer is preferably a polyester film a surface of which islubrication processed (lubrication processed PET), as it is easilypeeled from the magnetic layer after hot pressing.

———Hot Press———

The method for hot pressing is suitably selected depending on theintended purpose without any restriction. For example, it is performedby sandwiching stacked layers of the magnetic layer, the convex-concaveforming layer and the pattern transferring layer with a laminator orpress the stacked layers from the both sides thereof, then heating andpressing the same.

As a result of hot pressing, the surface configuration (convex-concavepattern) of the pattern transferring material is transferred to surfacesof the convex-concave forming layer and magnetic layer, and also theconvex-concave forming layer and the magnetic layer are directly bondedto each other without using an adhesive or the like.

The conditions for hot pressing are suitably adjusted depending on theintended purpose without any restriction. For example, the temperatureis preferably 80° C. to 190° C., the pressure is preferably 5 MPa to 20MPa, and the duration is preferably 1 minute to 20 minutes.

Bekk smoothness of the convex-concave forming layer after hot pressingis preferably 70 sec/mL or less, more preferably 1 sec/mL to 60 sec/mL.

When Bekk smoothness thereof is more than 70 sec/mL, the surfacelubricity of the convex-concave forming layer may be insufficient, andas a result, the magnetic sheet and a member which is brought intocontact with the magnetic sheet may be adhered.

According to the aforementioned step, the surface configuration of thepattern transferring material is transferred to the surfaces of theconvex-concave forming layer and magnetic layer at the same time as theconvex-concave forming layer and the magnetic layer are bonded to eachother. As a result, a magnetic sheet containing the magnetic layer andthe convex-concave forming layer is obtained.

The magnetic sheet obtained in the aforementioned manner has theconvex-concave forming layer a surface of which has the surfaceconfiguration transferred from the surface configuration (convex-concavesurface pattern) of the pattern transferring material and is roughened,and thus Bekk smoothness thereof is low and the lubricity thereof isexcellent.

According to the method for producing the magnetic sheet of the presentinvention, a surface configuration of the pattern transferring materialis transferred to surfaces of the convex-concave forming layer andmagnetic layer by hot pressing, and thus a surface of the convex-concaveforming layer is roughened, Bekk smoothness thereof is reduced, and thelubricity is improved.

Therefore, Bekk smoothness of the convex-concave forming layer can besuitably controlled in the desirable range regardless of the originalvalue of Bekk smoothness of the convex-concave forming layer, and thusthe selection of the material used for the convex-concave forming layeris widened. In addition, the control of Bekk smoothness can be performedeasily.

Moreover, as the convex-concave forming layer and the magnetic layer aredirectly bonded to each other by hot pressing, an adhesive layer isunnecessary, and thus a magnetic sheet can be easily and efficientlyproduced at low cost.

(Magnetic Sheet)

The magnetic sheet is suitably selected depending on the intendedpurpose without any restriction, provided that it is produced by themethod for producing a magnetic sheet mentioned earlier.

—Use—

The method for using the magnetic sheet of the present invention issuitably selected depending on the intended purpose without anyrestriction. For example, the magnetic sheet may be cut into a desirablesize, and disposed in an electronic equipment so that the magnetic sheetis placed adjacent to a noise source of the electronic equipment.

—Application—

The magnetic sheet of the present invention can be suitably applied forelectromagnetic noise depressors, electromagnetic wave absorbers,magnetic shielding, electronic equipments having IC tag functions suchas Radio Frequency Identification (RFID), and non-contact IC cards.Particularly, the magnetic sheet can be suitably used for RFIDfunctioned mobile phones.

EXAMPLES

Examples of the present invention will be explained hereinafter, butthese examples shall not be construed as limiting the scope of thepresent invention.

Example 1 Preparation of Curing Agent

Sulfonium anthimonate complexes respectively expressed by the formula1d, 1e and 1f (see JP-A No. 10-245378 for synthesis methods thereof)were each made dissolved in ethyl acetate to prepare a 10% by mass ethylacetate solution of each complex. A 10% solution of sodium borateexpressed by the formula 3 (see JP-A No. 10-310587 for a synthesismethod thereof) was prepared separately to above.

The 10% by mass solution of the sodium borate expressed by the formula 3was mixed in the 10% by mass ethyl acetate solution of the complex in anequimolecular amount at room temperature, and the mixture was stirredfor 30 minutes. Thereafter, the ethyl acetate layer was separated fromthe reacted mixed solution, and dried. The ethyl acetate was thenremoved under the reduced pressure. As a result, the sulfonium boratecomplex (4-hydroxyphenyl-methyl-1-naphthylmethyl sulfoniumtetrakis(pentafluorophenyl)borate) expressed by the formula 1a, thesulfornium borate complex(4-hydroxyphenyl-methyl-(2-methylbenzyl)sulfoniumtetrakis(pentafluorophenyl)borate) expressed by the formula 1b, and thesulfonium borate complex (4-hydroxyphenyl-methyl-benzylsulfoniumtetrakis(pentafluorophenyl)borate) expressed by the formula 1c were eachobtained as an evaporated residue.

The sulfonium borate complexes 1a and 1b were each subjected to massspectrometry (measuring device: AQUITY UPLC System, manufacturer: NihonWaters K.K.), an elemental analysis (measuring device: PHOENIX,manufacturer: EDAX Inc.), an IR analysis (measuring device: 7000e FT-IR,manufacturer: Varian Technologies Japan Limited), and ¹H-NMR analysis(measuring device: MERCURY PLUS, manufacturer: Varian Technologies JapanLimited). As a result, these complexes found to be targeted compounds.

Analysis Result of Sulfonium Borate Complex4-hydroxyphenyl-methyl-1-naphthylmethyl sulfoniumtetrakis(pentafluorophenyl borate) of Formula 1a <Result of MS Analysis>

M⁺=281 (sulfonium residue)M⁺=679 (borate residue)

<Result of Element Analysis> Actual Value: C, 52.51; H, 1.89 TheoreticalValue: C, 52.52; H, 1.78

<Result of IR Analysis (cm⁻¹)>

662 (C—S), 776, 980, 1088, 1276 (Ar—F), 1300, 1374, 1464, 1514, 1583,1643, 2881 (C—H), 2981 (C—H), 3107 (O—H)

<Result of ¹H-NMR Analysis (δ), See FIG. 1 (Using THF)>

2.6 (1H, (d)), 3.3 (3H, (a)), 5.3 (2H, (e)), 6.9 (2H, (c)), 7.6 (2H,(b)), 7.2 to 8.1 (7H, (f), (g), (h), (i), (j), (k), (l))

<Assignment of Proton>

Analysis Result of Sulfonium Borate Complex(4-hydroxyphenyl-methyl-(2-methylbenzyl)sulfoniumtetrakis(pentafluorophenyl)borate) of Formula 1b <Result of MS Analysis>

M⁺=245 (sulfonium residue)

M+=679 (borate residue)

<Result of Element Analysis>

Actual Value: C, 50.39; H, 1.77

Theoretical Value: C, 50.60; H, 1.80

<Result of IR Analysis (cm⁻¹)>

662 (C—S), 773, 980, 1088, 1276 (Ar—F), 1463, 1514, 1583, 1644, 2882(C—H), 2983 (C—H), 3109 (O—H)

<Result of ¹H-NMR Analysis (δ), See FIG. 2 (Using THF)>

2.3 (3H, (j)), 2.4 (1H, (d)), 3.3 (3H, (a)), 4.8 (2H, (e)), 7.0 (2H,(c)), 7.6 (2H, (b)), 7.0 to 7.4 (4H, (f), (g), (h), (i))

—Evaluation of Properties—

The sulfonium borate complexes 1a to 1c and sulfonium antimonatecomplexes 1d to 1f were each subjected to the measurement of thefluorine-ion concentration under the same temperature condition to thatof thermal cationic polymerization in the manner described below.Moreover, a thermal cationic polymerization composition was preparedusing each complex, and the prepared composition was subjected to adifferential thermal analysis (DSC) at the temperature rising rate of10° C./min.

—Measurement of Fluorine Ion Concentration—

To 10 mL of pure water, 0.2 g of each complex was added, and the mixturewas heated at 100° C. for 10 hours. Then, an amount of fluorine ionscontained in the supernatant was measured by an ion chromatographysystem (manufactured by Dionex Corporation). The results are shown inTable 1. It is preferred that the result be less than 10 ppm for thepractical use.

—DSC—

In 100 parts by mass of a fluid epoxy resin (Epikote 828, manufacturedby Japan Epoxy Resins Co., Ltd.) the complexes of Examples 1 and 2, andComparative Examples 1 to 4 were each mixed to prepare a thermalcationic polymerization composition. Here, the complexes of Examples 1and 2 were each mixed in an amount of 1 part by mass, the complex ofComparative Example 1 was mixed in an amount of 3 parts by mass, and thecomplexes of Comparative Examples 2 to 4 were each mixed in an amount of5 parts by mass. Each thermal cationic polymerization composition wassubjected to a differential thermal analysis (heating onset temperature,peak temperature, calorific value) by means of a thermal analysisequipment (DSC 5100, manufactured by Seiko Instruments Inc.). Theresults are shown in Table 1.

Note that, the heating onset temperature is temperature at which protonsare generated from the complex to initiate cationic polymerization. Thelow-temperature curing ability is more enhanced as the heat onsettemperature is lower. However, in this case, the storage stability tendsto decrease. Therefore, it is preferably 80° C. to 110° C. Moreover,when the thermal peak temperature is excessively low, the storagestability reduced. When it is excessively high, curing failures tend tooccur. Therefore, the thermal peak temperature is preferably 100° C. to140° C. The calorific value is corresponded to heat of the reaction, andis preferably 200 J/g or larger as curing failures tend to occur withthe excessively small calorific value.

TABLE 1 Reaction Exothermic F-ion onset peak Calorific concentrationtemperature temperature value Complex (ppm) (° C.) (° C.) (J/g) 1a 2.185 114 250 1b 2.3 105 134 320 1c 2.3 115 147 270 1d 160,000 83 118 2901e 170,000 106 135 300 1f 172,000 116 146 280

—Preparation of Magnetic Sheet—

At first, in a mixture of 270 parts by mass of toluene and 120 parts bymass of ethyl acetate, 83 parts by mass of acrylic rubber having epoxygroups (SG80H-3, manufactured by Nagase ChemteX Corporation, a numberaverage molecular mass of 150,000, a mass average molecular mass of350,000) serving as a binder, 23.1 parts by mass of an epoxy resin(Epikote 1031S, manufactured by Japan Epoxy Resins Co., Ltd.) serving asa binder, and 6.9 parts by mass of a cationic curing agent A(4-hydroxyphenyl-methyl-1-naphthylsulfoniumtetrakis(pentafluorophenyl)borate;Formula 1a) serving as a curing agent were made dissolved to prepare aresin composition. To the resin composition, 550 parts by mass of a flatmagnetic powder (JEM-S, manufactured by Mitsubishi MaterialsCorporation) serving as a magnetic powder was added, and mixed toprepare a magnetic sheet composition.

Next, the obtained magnetic sheet composition was applied onto apolyester film a surface of which had been lubricated processed (arelease PET) (38GS manufactured by Lintec Corporation, thickness of 38μm) as a substrate using a bar coater (i.e., the magnetic sheetcomposition was applied on the surface which had been lubricatedprocessed), to form a layer having a thickness of 100 μm to 200 μm.

Next, the applied coat was dried at room temperature for 10 minutes, andthen dried at 60° C. for 10 minutes. The release PET on thelubrication-processed surface of which a layer formed of the magneticsheet composition (a magnetic layer) had been formed was cut into thesize of 250 mm×250 mm, to thereby obtain 4 pieces of the release PET onthe lubrication-processed surface of which the magnetic layer had beenformed in the size of 250 mm×250 mm. Regarding two pieces of the releasePET on the lubrication-processed surface of which the magnetic layer inthe size of 250 mm×250 mm had been formed, the release PET was removedfrom the magnetic layer, to thereby obtain two pieces of the 250 mm×250mm magnetic layer. The two magnetic layers (each in the size of 250mm×250 mm) were placed and stacked on the magnetic layer side of therelease PET on the lubrication-processed surface of which the magneticsheet in the size of 250 mm×250 mm had been formed. Moreover, to theside of the lubrication-processed surface of this release PET, one pieceof the release PET on the lubrication-processed surface of which themagnetic layer in the size of 250 mm×250 mm had been formed was placedand stacked (so that the magnetic layers were facing each other), tothereby obtain a release PET in which four magnetic layers were stackedand both surfaces of the stacked layers were both held with a pair ofthe release PETs (i.e. the lubrication-processed surfaces of the tworelease PET were arranged so as to be in contact with the magneticlayers).

Next, on both surfaces of the stacked layers, which consisted of therelease PET, and the four magnetic layers stacked on another releasePET, two pieces of high quality paper (product name: OK Prince HighQuality 70, manufacturer: Oji Paper Co., Ltd., thickness: 100 Bekksmoothness: 6.2 sec/mL) used as buffer materials were respectivelystacked. Then, the stacked buffer materials were hot-pressed by means ofpress plates using a vacuum press (manufactured by KITAGAWA SEIKI Co.,Ltd.) under the conditions of the press-retaining temperature of 170°C., press-retaining duration (i.e. the time-period during which thepress-retaining temperature was maintained) of 5 minutes, press duration(i.e., the time required to come drown to 90° C. after reaching thepress-retaining temperature from 90° C.) of 38 minutes, andpress-pressure of 9 MPa. Thereafter, the two release PET were removedfrom the magnetic layer formed by curing the laminated four magneticlayers, to thereby obtain a magnetic sheet.

Examples 2 to 7 Preparation of Magnetic Sheet

Magnetic sheets of Examples 2 to 7 were each prepared in the same manneras in Example 1, provided that at least one of the formulated amount ofthe cationic curing agent A, the press retaining temperature, and thepress retaining duration were changed as presented in Table 2.

Example 8 Preparation of Magnetic Sheet

A magnetic sheet of Example 8 was prepared in the same manner as inExample 1, provided that as the curing agent, a cationic curing agent C(4-hydroxyphenyl-methyl-benzyl sulfoniumtetrakis(pentafluorophenyl)borate; the formula (1c)) was used instead ofthe cationic curing agent A (4-hydroxyphenyl-methyl-1-naphthylmethylsulfonium tetrakis(pentafluorophenyl)borate; the formula (1a)).

Examples 9 and 10 Preparation of Magnetic Sheet

Magnetic sheets of Examples 9 and 10 were each prepared in the samemanner as in Example 8, provided that at least one of the formulatedamount of the cationic curing agent C, the press-retaining temperature,and the press-duration were changed as presented in Table 3.

Example 11 Preparation of Magnetic Sheet

A magnetic sheet of Example 11 was prepared in the same manner as inExample 2, provided that as the curing agent, the cationic curing agentB (4-hydroxyphenyl-methyl-(2-methylbenzyl) sulfoniumtetrakis(pentafluorophenyl)borate; the formula (1b)) was used instead ofthe cationic curing agent A (4-hydroxyphenyl-methyl-1-naphthyl sulfoniumtetrakis(pentafluorophenyl)borate; the formula (1a)).

Example 12 Preparation of Magnetic Sheet

A magnetic sheet of Example 12 was prepared in the same manner as inExample 2, provided that as the magnetic powder, a flat magnetic powder(SP-1, manufactured by MATE CO., LTD.) was used instead of the flatmagnetic powder (JEM-S, manufactured by Mitsubishi MaterialsCorporation).

Example 13 Preparation of Magnetic Sheet

A magnetic sheet of Example 13 was prepared in the same manner as inExample 1, provided that as the magnetic powder, a flat magnetic powder(SP-1, manufactured by MATE CO., LTD.) was used instead of the flatmagnetic powder (JEM-S, manufactured by Mitsubishi MaterialsCorporation).

Example 14 Preparation of Magnetic Sheet

A magnetic sheet of Example 14 was prepared in the same manner as inExample 1, provided that as the magnetic powder, 900 parts by mass of aflat magnetic powder (EMS10, manufactured by Mitsubishi MaterialsCorporation) was used instead of 550 parts by mass of the flat magneticpowder (JEM-S, manufactured by Mitsubishi Materials Corporation), andthe formulated amount of the cationic curing agent A was changed from6.9 parts by mass to 8 parts by mass.

Example 15 Preparation of Magnetic Sheet

A magnetic sheet of Example 15 was prepared in the same manner as inExample 1, provided that the formulated amount of the flat magneticpowder (JEM-S, manufactured by Mitsubishi Materials Corporation) waschanged from 550 parts by mass to 1,600 parts by mass, the formulatedamount of the cationic curing agent A was changed from 6.9 parts by massto 10 parts by mass, and a convex-concave forming layer and apattern-transferring material were stacked in this order on one plane ofthe magnetic layer, which had bee formed by thermosetting the magneticsheet composition, followed by hot-pressing to transfer the pattern.

——Pattern Transferring——

A matte-surface treated polyester film (matte-processed PET) (productname: LUMIRRORX44-#25, manufacturer: Toray Industries, Inc., thickness:25 μm, Bekk smoothness: 101.8 sec/mL) serving as a convex-concaveforming layer, and a high quality paper (product name: OK Prince HighQuality 70, manufacturer: Oji Paper Co., Ltd., thickness: 100 μm, Bekksmoothness: 6.2 sec/mL) serving as a pattern transferring material werestacked on a surface of the magnetic layer so that the convex-concaveforming layer and the pattern transferring material were stacked in thisorder from the side of the magnetic layer.

Moreover, on the other surface of the magnetic layer, asurface-lubrication-processed polyester film (manufactured by LintecCorporation) serving as a release layer, and a high quality paper(product name: OK Prince High Quality 70, manufacturer: Oji Paper Co.,Ltd., thickness: 100 μm, Bekk smoothness: 6.2 sec/mL) serving as apattern transferring material were stacked, to thereby form a stackedbody.

Thereafter, the stacked body was subjected to hot pressing using avacuum press (manufactured by KITAGAWA SEIKI CO., LTD.) at temperatureof 170° C., and pressure of 9 MPa, for 10 minutes, by sandwiching thestacked body from both sides thereof with press plates to form themagnetic layer having a thickness of 80 μm. As a result, theconvex-concave forming layer and the magnetic layer were bonded, and atthe same time, the surface configuration of the pattern transferringmaterial was transferred to a surface of the laminate of theconvex-concave forming layer and the magnetic layer. The processesmentioned above were corresponded to the pattern transferring step.

The laminate, which had been hot-pressed, was cut into a sample size of250 mm×250 mm.

Then, the pattern transferring material and the release layer werereleased from the convex-concave forming layer and the magnetic layer tothereby obtain a magnetic sheet having a thickness of 105 μm.

Note that, the Bekk smoothness thereof after the hot-pressing was 26.3sec./mL.

Example 16 Preparation of Magnetic Sheet

A magnetic sheet of Example 16 was prepared in the same manner as inExample 1, provided that the formulated amount of the flat magneticpowder (JEM-S, manufactured by Mitsubishi Materials Corporation) as themagnetic powder was changed from 550 parts by mass to 1,200 parts bymass, the formulated amount of the cationic curing agent A was changedfrom 6.9 parts by mass to 10 parts by mass, and 10 parts by mass of redphosphorous (manufactured by Rinkagaku Kogyo Co., Ltd.) and 90 parts bymass of carboxylic acid amide-containing melamine cyanurate (MC-5F,manufactured by Sakai Chemical Industry Co., Ltd.) were further added.

Example 17 Preparation of Magnetic Sheet

A magnetic sheet of Example 17 was prepared in the same manner as inExample 1, provided that as the magnetic powder, 900 parts by mass of aflat magnetic powder (EMS 10, manufactured by Mitsubishi MaterialsCorporation) was used instead of 550 parts by mass of the flat magneticpowder (JEM-S, manufactured by Mitsubishi Materials Corporation), theformulated amount of the cationic curing agent A was changed from 6.9parts by mass to 8 parts by mass, and 10 parts by mass of redphosphorous (manufactured by Rinkagaku Kogyo Co., Ltd.) and 90 parts bymass of carboxylic acid amide-containing melamine cyanurate (MC-5F,manufactured by Sakai Chemical Industry Co., Ltd.) were further added.

Comparative Example 1 Preparation of Magnetic Sheet

A magnetic sheet of Comparative Example 1 was prepared in the samemanner as in Example 1, provided that as the curing agent, animidazole-based curing agent (HX3748, manufactured by Asahi KaseiChemicals Corporation) was used instead of the cationic curing agent A(4-hydroxyphenyl-methyl-1-naphthyl sulfonium,tetrakis(pentafluorophenyl)borate; the formula (1a)).

Comparative Example 2 Preparation of Magnetic Sheet

A magnetic sheet of Comparative Example 2 was prepared in the samemanner as in Example 2, provided that as the curing agent, animidazole-based curing agent (HX3748, manufactured by Asahi KaseiChemicals Corporation) was used instead of the cationic curing agent A(4-hydroxyphenyl-methyl-1-naphthyl sulfoniumtetrakis(pentafluorophenyl)borate; the formula (1a)).

Comparative Example 3 Preparation of Magnetic Sheet

A magnetic sheet of Comparative Example 3 was prepared in the samemanner as in Example 3, provided that as the curing agent, animidazole-based curing agent (HX3748, manufactured by Asahi KaseiChemicals Corporation) was used instead of the cationic curing agent A(4-hydroxyphenyl-methyl-1-naphthyl sulfoniumtetrakis(pentafluorophenyl)borate; the formula (1a)).

Comparative Example 4 Preparation of Magnetic Sheet

A magnetic sheet of Comparative Example 4 was prepared in the samemanner as in Example 4, provided that as the curing agent, animidazole-based curing agent (HX3748, manufactured by Asahi KaseiChemicals Corporation) was used instead of the cationic curing agent A(4-hydroxyphenyl-methyl-1-naphthyl sulfoniumtetrakis(pentafluorophenyl)borate; the formula (1a)).

Comparative Example 5 Preparation of Magnetic Sheet

A magnetic sheet of Comparative Example 5 was prepared in the samemanner as in Example 5, provided that as the curing agent, animidazole-based curing agent (HX3748, manufactured by Asahi KaseiChemicals Corporation) was used instead of the cationic curing agent A(4-hydroxyphenyl-methyl-1-naphthyl sulfoniumtetrakis(pentafluorophenyl)borate; the formula (1a)).

Comparative Example 6 Preparation of Magnetic Sheet

A magnetic sheet of Comparative Example 6 was prepared in the samemanner as in Example 6, provided that as the curing agent, animidazole-based curing agent (HX3748, manufactured by Asahi KaseiChemicals Corporation) was used instead of the cationic curing agent A(4-hydroxyphenyl-methyl-1-naphthyl sulfoniumtetrakis(pentafluorophenyl)borate; the formula (1a)).

Comparative Example 7 Preparation of Magnetic Sheet

A magnetic sheet of Comparative Example 7 was prepared in the samemanner as in Comparative Example 1, provided that the press-retainingduration and the press duration were both changed as presented in Table6.

Comparative Example 8 Preparation of Magnetic Sheet

A magnetic sheet of Comparative Example 8 was prepared in the samemanner as in Example 1, provided that as the curing agent, anantimony-based cationic curing agent (San-Aid SI-60L, manufactured bySanshin Chemical Industry Co., Ltd.) was used instead of the cationiccuring agent A (4-hydroxyphenyl-methyl-1-naphthyl sulfoniumtetrakis(pentafluorophenyl)borate; the formula (1a)).

[Magnetic Permeability]

At first, a ring sample, which had been cut out so as to have an outerdiameter of 7.05 mm, and an inner diameter of 2.945 mm, was prepared. Alead-wire was then wound around the ring sample 5 times, and then it wassoldered to a terminal. Here, the length between the bottom of theterminal and the bottom of the ring sample was set 20 mm. Then, theinductance and resistance thereof at 1 MHz were measured using animpedance analyzer (4294A, manufactured by Agilent Technologies, Inc.),and the obtained values were converted into magnetic permeability.

Note that, μ′ denotes a real part of complex magnetic permeability.

The properties of μ′ are different depending on the intended use of amagnetic sheet. For example, in the case where it is used for improvinga correspondence of a RFID device, it is preferred that the value of ishigh and the value of μ″ (an imaginary part of complex magneticpermeability) is low at the frequency of 20 MHz or lower.

Moreover, the magnetic sheet of the present invention is usable in thefrequency range of KHz to GHz.

[Reliability Test] —Change in Thickness—

At first, a thickness of the magnetic sheet was measured. Then, themagnetic sheet was placed in an oven, and heated at 85° C., and 60% RHfor 96 hours. After taking the magnetic sheet out from the oven, thethickness of the magnetic sheet was measured again, and a rate of thechange in the thickness of the magnetic sheet before and after heatingwas measured.

[Fluorine (F⁻¹) Ion Elution Test]

A magnetic sheet sample (about 0.2 g) of Example 1 and a magnetic sheetsample (about 0.2 g) of Comparative Example 8 were each separately addedto a PP container having 10 mL of ultrapure water. The container wasthen placed in an oven set at 100° C., and was left there for 10 hours.Thereafter, 10 mL of an extract was taken out from the container, andwas subjected to the measurement of a fluorine (F⁻¹) ion concentration(μg/mL). Based on the obtained fluorine (F⁻¹) ion concentration (μg/mL)of the extract, a fluorine (F⁻¹) ion concentration (μg/g) per g of themagnetic sheet sample was calculated using the following formula (1).The results are shown in Table 7.

(Fluorine (F⁻¹) ion concentration (μg/mL)−blank average value(μg/mL))×10 (mL)/(weight of magnetic sheet sample (g))  <Formula (1)>

[Corrosion Test]

A magnetic sheet sample (about 0.2 g) of Example 1 and a magnetic sheetsample (about 0.2 g) of Comparative Example 8 were each separately addedto a plastic container (DESCUP) containing 50 mL of tap water. Then, thecontainer was placed in an oven set at 85° C. and 85% RH, and was leftthere for 16 hours. Thereafter, the magnetic sheet sample was taken outfrom the plastic container containing 50 mL of tap water, and thecross-sectional plane of the magnetic sheet was observed under amicroscope. The results are shown in FIGS. 3A and 3B, and Table 7.

[Combustion Test]

Magnetic sheet samples of Example 16 and Example 17 were both subjectedto the combustion test in the following manner.

As the combustion test, a UL94V test (a combustion test for a plasticmaterial of machinery parts) was carried out. The UL94V test was amethod for evaluating flame resistance based on the afterflame time,after placing a certain size of a sample directly in a flame of a burnerfor 10 seconds with the sample held vertically. The results wereevaluated based on the following criteria.

—Evaluation Criteria—

V-0: The afterflame time of each sample was 10 seconds or shorter, andthe total afterflame time of 5 samples was 50 seconds or shorter.

V-1: The afterflame time of each sample was 30 seconds or shorter butlonger than 10 seconds, and the total afterflame time of 5 samples was250 seconds or shorter but longer than 50 seconds.

V-2: The combustion time (afterflame time?) was the same as V-1, butthere were flame-droppings.

NG: The flame resistance was low, and it did not comply with thestandard of UL94V.

Here, “afterflame time” means a length of time showing how long flamecombustion of the test sample continues after an ignition source ismoved away.

[Method of Measuring LOSS Properties (Transmission Loss)]

Magnetic sheets of Examples 16 and 17 were each subjected to themeasurement of LOSS properties (transmission loss) in the followingmanner.

For measurement of transmission loss, a microstripline having animpedance Z of 50Ω was used. The use of the microstripline line was acommonly used method for measuring transmission loss of adjacent noise,because of its structure suitable for mounting a surface-mountingcomponent and production easiness. The shape of the microstripline 2used is shown in FIG. 4. The transmission loss was measured in such amanner that a linear conductor path was provided on a surface of aninsulator substrate, and a magnetic sheet was placed on the conductorpath for measurement. Both ends of the conductor path were connected toa network analyzer 1. Then, a reflection amount (dB) and a permeationamount (dB) from the part where an electromagnetic wave absorptionmaterial was mounted, was measured with respect to incident wave shownby an arrow, and the difference between the reflection amount (dB) andthe permeation amount (dB) was obtained as a loss amount, and thus atransmission loss (absorptance) was obtained (incident amount=reflectionS11+loss+permeation S21). Specifically, a known amount of anelectromagnetic wave was incident, the reflection amount S11 and thepermeation amount S21 were measured, and then calculated to obtain aloss amount.

The thicker the magnetic sheet was, the higher the transmission loss ofthe microstripline became. Generally, a magnetic sheet having a thinthickness and high transmission loss is desired.

TABLE 2 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Magnetic Flat magnetic550 550 550 550 550 550 550 powder powder (JEM-S) (mass part) BinderAcrylic rubber 83 83 83 83 83 83 83 (mass part) (SG80H-3) Epoxy resin23.1 23.1 23.1 23.1 23.1 23.1 23.1 (1031S) Curing Cationic curing 6.96.9 6.9 4.0 4.0 2.0 2.0 agent agent A Hot press Press-retaining 170 150130 170 150 170 150 temperature (° C.) Press-retaining 5 5 5 5 5 5 5duration (min.) Press duration 38 20 16 38 20 38 20 (min.) MagneticInitial magnetic 40.4 38.9 38.2 41.0 40.2 40.9 40.1 permeabilitypermeability μ′ (1 MHz) Reliability Thickness before 293 321 322 297 299300 301 test test (μm) Thickness after 294 325 330 300 303 305 307 test(μm) Thickness 0.34 1.25 2.48 1.01 1.34 1.67 1.99 changing rate (%)

TABLE 3 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13 Magnetic Flat magnetic550 550 550 550 NA NA powder powder (JEM-S) (mass part) Flat magnetic NANA NA NA 550 550 powder (SP-1) Binder Acrylic rubber 83 83 83 83 83 83(mass part) (SG80H-3) Epoxy resin 23.1 23.1 23.1 23.1 23.1 23.1 (1031S)Curing Cationic curing NA NA NA NA 6.9 6.9 agent agent A Cationic curingNA NA NA 6.9 NA NA agent B Cationic curing 6.9 6.9 10.0 NA NA NA agent CHot press Press-retaining 170 150 150 150 150 170 temperature (° C.)Press-retaining 5 5 5 5 5 5 duration (min.) Press duration 38 20 20 2020 38 (min.) Magnetic Initial magnetic 42.0 41.3 38.9 42.0 101.5 103.3permeability permeability μ′ (1 MHz) Reliability Thickness before 295300 308 298 291 287 test test (μm) Thickness after 296 304 309 302 296290 test (μm) Thickness 0.34 1.33 0.32 1.34 1.72 1.05 changing rate (%)

TABLE 4 Ex. 14 Ex. 15 Ex. 16 Ex. 17 Magnetic powder Flat magnetic 900 NANA 900 (mass part) powder (EMS10) Flat magnetic NA 1,600 1,200 NA powder(JEM-S) Binder (mass Acrylic rubber 83 83 83 83 part) (SG80H-3) Epoxyresin 23.1 23.1 23.1 23.1 (1031S) Curing agent Cationic curing 8 10 10 8agent A Red phosphorus Red phosphorus NA NA 10 10 Carboxylic acid MC-5FNA NA 90 90 amide-containing melamine cyanurate Hot pressPress-retaining 170 170 170 170 temperature (° C.) Press-retaining 5 5 55 duration (min.) Press duration 38 38 38 38 (min.) Magnetic Initialmagnetic 115.1 46.2 41.3 93.4 permeability permeability μ′ (1 MHz)Reliability test Thickness before 99 105 99 108 test (μm) Thicknessafter 100 107 100 109 test (μm) Thickness 1.01 1.90 1.01 0.93 changingrate (%) Combustion test result NA NA V-0 V-0

TABLE 5 Comp. Comp. Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Magnetic powderFlat magnetic 550 550 550 550 (mass part) powder (JEM-S) Binder (massAcrylic rubber 83 83 83 83 part) (SG80H-3) Epoxy resin 23.1 23.1 23.123.1 (1031S) Curing agent Imidazole-based 6.9 6.9 6.9 4.0 curing agent(HX3748) Hot press Press-retaining 170 150 130 170 temperature (° C.)Press-retaining 5 5 5 5 duration (min.) Press duration 38 20 16 38(min.) Magnetic Initial magnetic 40.5 39.9 38.9 34.6 permeabilitypermeability μ′ (1 MHz) Reliability test Thickness before 278 283 294336 test (μm) Thickness after 284 293 308 347 test (μm) Thickness 2.163.53 4.76 3.27 changing rate (%)

TABLE 6 Comp. Comp. Comp. Comp. Ex. 5 Ex. 6 Ex. 7 Ex. 8 Magnetic powderFlat magnetic 550 550 550 550 (mass part) powder (JEM-S) Binder (massAcrylic rubber 83 83 83 83 part) (SG80H-3) Epoxy resin 23.1 23.1 23.123.1 (1031S) Curing agent Imidazole-based 4.0 2.0 6.9 NA curing agent(HX3748) Antimony-based NA NA NA 6.9 curing agent (San-Aid SI-60L) Hotpress Press-retaining 150 170 170 170 temperature (° C.) Press-retaining5 5 10 5 duration (min.) Press duration 20 38 43 38 (min.) MagneticInitial magnetic 32.3 33.0 41.0 40.8 permeability permeability μ′ (1MHz) Reliability test Thickness before 341 340 282 303 test (μm)Thickness after 359 406 286 307 test (μm) Thickness 5.28 19.41 1.42 1.32changing rate (%)

TABLE 7 Comp. Ex. 1 Ex. 8 Magnetic powder Flat magnetic 550 550 (masspart) powder (JEM-S) Binder (mass Acrylic rubber 83 83 part) (SG80H-3)Epoxy resin 23.1 23.1 (1031S) Curing agent Cationic curing 6.9 NA agentA Antimony-based NA 6.9 curing agent (San-Aid SI-60L) Hot pressPress-retaining 170 170 temperature (° C.) Press-retaining 5 5 duration(min.) Press duration 38 38 (min.) Magnetic Initial magnetic 40.4 40.8permeability permeability μ′ (1 MHz) Reliability test Thickness 293 303before test (μm) Thickness after 294 307 test (μm) Thickness 0.34 1.32changing rate (%) Elution test F-ion 1.168 13.195 concentration (μm/mL)F-ion 55.597 626.820 concentration (μg/g) Corrosion test Cross-sectionNo Corrosion observation corrosion at the edge

TABLE 8 Loss properties Example 16 Example 17 100 MHz 2.58 3.25 500 MHz22.1 28.4  1 GHz 55.48 62.1

From the results shown in Tables 2 to 6, it was found that the magneticsheets of Examples 1 to 13, in which the curing agents each containing asulfonium borate complex (the cationic curing agents A to C) were used,had excellent size-stability in the high-temperature high-humidityenvironment compared to the magnetic sheets of Comparative Examples 1 to8 in which the imidazole-based curing agent or antimony-based curingagent was used as the curing agent. This can be seen from the fact thatthe rate of the change in the thickness in the reliability test ofExamples is smaller than that of Comparative Examples, comparing thecombination of Example and Comparative Example where only the usedcuring agents are different between them in the preparation condition ofthe magnetic sheet (e.g. Example 1 and Comparative Example 1; Example 1and Comparative Example 8; Example 2 and Comparative Example 2; Example3 and Comparative Example 3; Example 4 and Comparative Example 4;Example 5 and Comparative Example 5; Example 6 and Comparative Example6; Example 8 and Comparative Example 1; Example 8 and ComparativeExample 8; Example 9 and Comparative Example 2; Example 11 andComparative Example 2).

Moreover, from the results shown in FIGS. 3A and 3B, and Table 7, it wasfound that the magnetic sheet of Example 1 could suppress elution offluorine ions more than the magnetic sheet of Comparative Example 8, sothat the magnetic sheet of Example 1 could prevent corrosion of themagnetic sheet. Note that, it is assumed that the corrosion seen on thesurface of the magnetic sheet of FIG. 3B is the magnetic powder corrodedby impurity ions (fluorine ions). As mentioned above, the magnetic sheetof Example 1 can prevent corrosion of wirings even when it is usedaround the wirings, as the magnetic sheet of Example 1 prevents elutionof fluorine ions.

Moreover, it was found that the magnetic sheets of Examples 1 to 17 weresuitably applied for RFID functioned mobile phones.

Furthermore, it was found that the magnetic sheet of Example 15 wasusable even through it contained a large amount of the magnetic powder,which would easily cause cracking. This is because the magnetic sheet ofExample 15 has a convex-concave forming layer (PET), and thus themagnetic sheet of Example 15 could maintain the shape thereof (as it wasprotected by the convex-concave forming layer (PET)).

Examples 16 and 17 showed high flame resistance in the combustion test(Table 4), and high electromagnetic wave-absorbing abilities in themeasurement of LOSS properties (transmission loss) (Table 8).

The magnetic sheet of the present invention is suitably used for, forexample, an electromagnetic noise depressor, an electromagnetic waveabsorber, a magnetic shielding material, an electronic equipment havingan IC tag function such as RFID and non-contact IC card, and isparticularly suitably used for a RFID functioned mobile phone.

What is claimed is:
 1. A method for preparing a magnetic sheet,comprising: applying a magnetic sheet composition onto a substrate;drying the magnetic sheet composition applied onto the substrate; andthermosetting the dried magnetic sheet composition, wherein the magneticsheet composition comprises a binder, magnetic powder, and a curingagent, and wherein the binder contains a thermosetting organic resin,and the curing agent contains a sulfonium borate complex expressed byGeneral Formula 1:

where R₁ is an aralkyl group, R₂ is a lower alkyl group, X is a halogenatom, and n is an integer of 0 to
 3. 2. The method for preparing amagnetic sheet according to claim 1, wherein R₁ is a benzyl group, ano-methyl benzyl group, or a (1-naphthyl)methyl group.
 3. The method forpreparing a magnetic sheet according to claim 1, wherein R₂ is a methylgroup.
 4. The method for preparing a magnetic sheet according to claim1, wherein the magnetic sheet composition comprises the sulfonium boratecomplex in an amount of 2 parts by mass to 15 parts by mass relative to106.1 parts by mass of the binder.
 5. The method for preparing amagnetic sheet according to claim 1, wherein the magnetic sheetcomposition further comprises a flame retardant, and the flame retardantcontains carboxylic acid amide-containing melamine cyanurate.
 6. Use ofa magnetic sheet composition for a magnetic sheet: wherein the magneticsheet composition comprises a binder, magnetic powder and a curing agentand wherein the binder contains a thermosetting organic resin, and thecuring agent contains a sulfonium borate complex expressed by GeneralFormula 1:

where R₁ is an aralkyl group, R₂ is a lower alkyl group, X is a halogenatom, and n is an integer of 0 to
 3. 7. Use according to claim 6,wherein R₁ is a benzyl group, an o-methyl benzyl group, or a(1-naphthyl)methyl group.
 8. Use according to claim 6, wherein R₂ is amethyl group.
 9. Use according to claim 6, wherein the magnetic sheetcomposition comprises the sulfonium borate complex in an amount of 2parts by mass to 15 parts by mass relative to 106.1 parts by mass of thebinder.
 10. Use according to claim 6, wherein the magnetic sheetcomposition further comprises a flame retardant, and the flame retardantcontains carboxylic acid amide-containing melamine cyanurate.